Besides exercising too little and eating too much—especially too much over-processed, high-calorie food—there’s another possible reason that many Americans are overweight, says Amy Joy Lanou, PhD, director of human nutrition at the Physicians Committee for Responsible Medicine in Washington, DC: “People are eating meat from animals that have been given hormones and antibiotics to fatten them up. Those chemicals are concentrated in the animals’ fat and passed on to whoever eats it.” The connection? Bovine hormones are growth promoters. If enough growth promoters are now in the food supply, they could be affecting the weight of adults and kids, about a third of whom are now obese.

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“It stands to reason,” says Lanou. “However,” she emphasizes, “we don’t have solid evidence of the link.” (Lanou personally believes there may be a more direct connection between eating meat and gaining weight. One way hormones make animals larger is by adding fat. “Eating fattier meat could itself add pounds,” she says. In short: Eating fat makes you fat.)

The hormone connection is definitely controversial. Still, it’s being scrutinized by Samuel Epstein, MD, professor at the University of Illinois School of Public Health in Chicago and the chair of Chicago’s Cancer Prevention Coalition. “Sex hormones—particularly estradiol, which is used to fatten cattle—can result in high residues in meat. Children are especially sensitive to hormonal influences. It’s possible that the childhood obesity epidemic is linked to hormone exposure,” he says. But the connection is complex. Still, growth hormones “increase cattle weight by about 10 percent. So it’s not surprising that eating meat contaminated with high levels of hormones could lead to weight gain.”

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Concern over hormones in food isn’t new. But the link to cancers in adulthood is stronger than the link to obesity. Cancer worries have led the European Union (EU) to ban hormone-treated American beef since 1989. Lester Crawford, DVM, PhD, of the Food and Drug Administration, calls the ban a political maneuver to keep US meat out of Europe. “If you look at the hormone levels in cattle production, there is no long-lasting effect. That requires pharmacologically

active levels, and the residue in meat is miniscule,” he says.

But others say that there are high levels in meat. “Part of the problem is that, while the hormones are supposed to be inserted via a pellet in the animal’s ear, the pellet is often placed in a muscle instead, where it can cause up to 100-fold greater estradiol levels in the meat,” Epstein asserts.

Don’t expect any definitive conclusions soon. “Since it is impossible to experiment on humans—and since there haven’t been any rigorous studies looking specifically at the connection between meat consumption and obesity—it’s impossible to prove a correlation,” says Carlos

Sonnenschein, MD, a professor at Tufts University School of Medicine and one of four Americans on the EU panel that assessed the risks of hormone-treated meat. “It stands to reason, however, that if children eat meat that contains hormones, it would increase their weight. It is safer not to be exposed to these hormones. They could upset the homonal and metabolic balance in the body. The same is true for pregnant women and other adults.”